Specifications and software structures of terminals, for example, mobile terminals, are kept secret. The security of confidential information, for example, authentic cryptographic keys, may be ensured using secure modules (e.g., tamper-resistant modules) whose integrity is ensured. One example of the secure modules is a subscriber identity module (SIM) card.
For example, for communication with a terminal, an external apparatus determines whether or not received communication content is encrypted with an authentic cryptographic key whose integrity is ensured, thereby determining whether or not the communication content is authentic.
Related art is disclosed in Japanese Laid-open Patent Publication No. 2004-129227 and Japanese Patent No. 4408601.